On this date in 1683 the English politician and philosopher Algernon Sidney (or Sydney) was beheaded to uphold (so he conceived it) “the common rights of mankind, the laws of this land, and the true Protestant religion, against corrupt principles, arbitrary power, and Popery.”

He was one of the 17th century’s great philosophers of republicanism, and his Discourses Concerning Government was more influential in his lifetime than the work of his contemporary (and fellow-Whig*) John Locke.

Although the pen might be mightier than the sword, Sydney himself did not eschew the more literal form of combat and entered a triumphant battlefield for the Roundheads at Marston Moor. But despite penning a strong defense of assassinating despots,** Sidney’s disapproval of the proceedings against King Charles I — a trial at which Sidney, now a parliamentarian, sat as a commissioner — kept him free of the whiff of regicide.

The Republic that prevailed after King Charles’s scaffold, and in which he continued as an MP, was the closest thing Sidney would experience to the political order his writings expounded. When Parliament was forcibly disbanded in 1653 to give over to Cromwell’s rule, Sidney (like his friend and mentor Henry Vane) would not quit the legislature until General Harrison physically seized him. He sorely provoked the interregnum state thereafter by staging a pointed performance of that tyrannicidal play, Julius Caesar … starring himself as Brutus.

Away on the continent when the monarchy was restored in 1660, Sidney would not lay eyes on native soil again until 1677, when he secured a royal mulligan that also spared him the fruits of various plots he had cogitated while in exile to re-depose the Stuarts with the aid of France or the Netherlands. But he returned as one of the leading men of a Whig faction that increasingly courted the ire of the crown and from whose machinations the arch-republican was in no way dissuaded.

Sidney’s prosecution as a party to the Rye House Plot to murder King Charles II helped to earn the new Lord Chief Justice George Jeffreys his reputation as a notorious hanging judge: promoted to the post weeks earlier as a reward for his prosecution of Sidney’s alleged conspirator Lord Russell, Jeffreys stacked the trial against the defendant leading Sidney to issue from the scaffold a lengthy disquisition on the iniquities of the court. (Notably, Jeffreys circumvented a standard requiring two witnesses to prove treason by ruling that Jeffreys’ own writings made their author a “second witness”.)

* Locke had no appetite for the noble martyrdom act pulled by the likes of Sidney and Lord Russell. He fled to the Netherlands during the Rye House Plot crackdown, only returning to England with the Glorious Revolution.

Honour and riches are justly heaped upon the heads of those who rightly perform their duty [of tyrannicide], because the difficulty as well as the excellency of the work is great. It requires courage, experience, industry, fidelity, and wisdom. “The good shepherd,” says our Saviour, “lays down his life for his sheep.” The hireling, who flies in time of danger, is represented under an ill character; but he that sets himself to destroy his flock, is a wolf. His authority is incompatible with their subsistence. And whoever disapproves tumults, seditions, or war, by which he may be removed from it, if gentler means are ineffectual, subverts the foundation of all law, exalts the fury of one man to the destruction of a nation, and giving an irresistible power to the most abominable iniquity, exposes all that are good to be destroyed, and virtue to be utterly extinguished.